The present invention relates to a method for the benefication of coal prior to its use in combustion, liquefaction or gasification processes. Much of the bituminous and lignite coal in this country tends to agglomerate and cake when heated to high temperatures. The method of the present invention is an uncomplicated and improved procedure for converting such coal to a noncaking material.
In gasification, liquefaction, combustion and hydropyrolysis processes for converting coal and other carbonaceous materials to more useful forms, elevated temperatures are used. These temperatures are often at and above those at which the carbonaceous material becomes sticky and begins to cake or agglomerate. A hydropyrolysis process that employes high temperatures and high flow rates through small reactor passageways is disclosed in the assignee's copending patent applications U.S. DOE Docket No. S-50,424 entitled "Reactor and Method for Hydrocracking Carbonaceous Material" to Duncan et al., Ser. No. 15,257 filed Feb. 26, 1979 and U.S. DOE Docket No. S-50,975 entitled "Process for Hydrocracking Carbonaceous Material to Provide Fuels or Chemical Feed Stock" to Duncan, Ser. No. 15,258 filed Feb. 26, 1979. In processes and hydropyrolysis reactors like those described in these patent applications, the coal is heated to a temperature above 1200.degree. F. while entrained within a high velocity gas stream. The agglomeration of coal can soon plug the tubular flow passageways leading to and in such reactors.
Although the above-mentioned hydropyrolysis processes are quite susceptible to interruption through plugging with caking coal, the present invention may have application in various other coal uses. For instance, the transport of coal by mechanical conveyors or fluidization is impeded by agglomeration. The feed and removal of coal from both fixed and fluidized-bed gasifiers, liquefiers and combustors are greatly facilitated if the problem of agglomeration can be minimized or eliminated.
Prior processes for decaking coal have required the use of extreme temperatures and pressures to avoid extended periods of processing time. Temperatures of 500.degree. F. or above and pressures of 300-1000 psi have been used. Alternatively, comparative Example I of the present application shows that heating to moderate temperatures of about 300.degree. F. for an extended period of about 5 hours or more can render coal noncaking.